In manufacturing structural elements such as metal machine parts, it is often necessary that the element have a finished surface of particular design and shape. As an example, machine elements which are adapted to cooperate in a sliding, gearing or camming relation must have cooperating surfaces of precise shape. Where these surfaces are straight, circular, or of some other common shape, the machining or surfacing is not too difficult. Where, however, the desired surface of the element is a complicated curve, as for example, one having an ever changing radius of curvature, the machining thereof becomes both difficult and expensive.
If the desired surface is an external one, a lathe or similar cutting machine may be used. Also, where tolerances are not of critical importance, a milling machine may be used. A milling machine is advantageous in that it can mill both external and internal surfaces on a workpiece.
Where tolerances are critical, however, a grinding machine is usually employed. Grinding machines can produce extremely accurate surfaces; but when these surfaces are of unusual shape, the expense of constructing the machine to perform the particular grinding operation is often prohibitive. It may, for example, take a number of separate grinding operations to produce a particular complex surface with each of the grinding operations requiring that the workpiece be fed through a separate grinding machine. In addition, the feeding of the workpiece relative to the grinding wheel is difficult to control both with regard to its direction of movement and rate of feed past the grinding wheel. Different sized grinding wheels generally require that the workpiece be fed through different paths in order to produce the same surface. Similarly, as the grinding wheel becomes worn during a grinding operation, adjustments in the direction of movement of the workpiece must be made in order to maintain the desired surface cut. This is especially true where a curved surface is desired. In addition to the problems encountered with different sized grinding wheels, any changes in rate of feed of the workpiece relative to the grinding wheel adversely affects both efficiency of operation and the quality of the finished surface. Different grinding rates produce different surface finishes. This, in turn, necessitates further processing of the workpiece to obtain uniformity.
One solution to these requirements is the type of cam controlled grinding machine described in U.S. Pat. Nos. 3,663,188, 3,800,621 and 3,822,511 which are assigned to the present assignee. These patents are incorporated herein by reference. As disclosed, for example in FIGS. 1 and 2 of the '188 and '621 patents such devices include an annular cam member 1 having a surface 3 that is identical to a surface 9 of a workpiece 7 to be ground. The workpiece is fixed relative to the cam member so that as the cam member is moved the workpiece moves through a path corresponding to contoured surface 3 of the cam member; and a grinding wheel 8 engages the surface of the workpiece as it is fed along this path. To move the workpiece through the desired path, a rotating drive follower 2 engages contoured surface 3 of the cam member.
In accordance with the teachings of those inventions, cam member 1 is supported by being bolted to a support 22 that is attached to the lower end of a spindle 21. The upper end of the spindle has another support 23 to which workpiece 7 is attached for the grinding operation. The spindle is mounted within a housing 25 so that it is free to rotate about its longitudinal axis and is also free to move laterally during this rotation along a path dictated by the internal surface 3 of the cam member. For this purpose, the spindle includes a circular bearing plate 24 attached to the spindle intermediate its ends with the peripheral portion of the bearing plate disposed within housing 25. The housing includes a plurality of upper and lower pockets 26 and 27 facing the opposite sides of the bearing plate.
As disclosed in the '188 and '621 patents, pockets 26, 27 are supplied with air pressure to act against the opposed sides of the bearing plate in the housing 25. The sizes of the upper and lower pockets can be dimensioned and/or the air pressure regulated to compensate for the weight of the spindle and attached structure to cause the bearing plate to float within housing 25. Alternatively, hydraulic pressure may be provided; or air pressure may be supplied against the underside of the bearing plate while oil is provided for maintaining a sliding relationship of the upper side of the plate with the opposed wall of the housing. With either type of construction, a thrust bearing effect is produced which permits rotation of the spindle and lateral movement in a plane perpendicular to its axis of rotation with a minimum amount of friction.